Expose pthread feature flag

The code was able to use pthread destructors rather than C++ thread
local destructors.  This removes the dependence on a C++ .so on linux.
However, this is not stable on other platforms such as Apple. Where the
C++ thread local state can be cleared before the pthread destructor
runs.

.github/workflows/main.yml

@@ -38,16 +38,23 @@ jobs:
             build-type: Debug
             build-only: yes
           # Add the self-host build
-          - os: ubuntu-latest
+          - os: "ubuntu-latest"
             build-type: Debug
             self-host: true
+          # Extra build to check using pthread library for destructing local state.
+          - os: "ubuntu-latest"
+            variant: "Ubuntu (with pthread destructors)."
+            dependencies: "sudo apt install ninja-build"
+            build-type: Debug
+            self-host: true
+            extra-cmake-flags: "-DSNMALLOC_USE_PTHREAD_DESTRUCTORS=On -DCMAKE_CXX_COMPILER=clang++-10 -DCMAKE_C_COMPILER=clang-10"
           # Add an extra element to the matrix that does a build with clang 12
           # but doesn't run tests.
           - os: "freebsd-13.0"
             variant: Clang 12 (Build only)
             extra-cmake-flags: "-DCMAKE_CXX_COMPILER=clang++12"
             build-only: yes
-          - os: ubuntu-latest
+          - os: "ubuntu-latest"
             variant: Clang 10 libstdc++ (Build only)
             dependencies: "sudo apt install ninja-build"
             extra-cmake-flags: "-DCMAKE_CXX_COMPILER=clang++-10 -DCMAKE_C_COMPILER=clang-10 -DCMAKE_CXX_FLAGS=-stdlib=libstdc++"

CMakeLists.txt

@@ -19,6 +19,7 @@ option(SNMALLOC_QEMU_WORKAROUND "Disable using madvise(DONT_NEED) to zero memory
 option(SNMALLOC_OPTIMISE_FOR_CURRENT_MACHINE "Compile for current machine architecture" Off)
 set(SNMALLOC_STATIC_LIBRARY_PREFIX "sn_" CACHE STRING "Static library function prefix")
 option(SNMALLOC_USE_CXX17 "Build as C++17 for legacy support." OFF)
+option(SNMALLOC_USE_PTHREAD_DESTRUCTORS "Build using pthread destructors. Reduces the system dependencies, but may interact badly with C++ on some platforms." OFF)
 
 # malloc.h will error if you include it on FreeBSD, so this test must not
 # unconditionally include it.
@@ -150,6 +151,10 @@ if(SNMALLOC_PLATFORM_HAS_GETENTROPY)
   target_compile_definitions(snmalloc_lib INTERFACE -DSNMALLOC_PLATFORM_HAS_GETENTROPY)
 endif()
 
+if(SNMALLOC_USE_PTHREAD_DESTRUCTORS)
+  target_compile_definitions(snmalloc_lib INTERFACE -DSNMALLOC_USE_PTHREAD_DESTRUCTORS)
+endif()
+
 if(CONST_QUALIFIED_MALLOC_USABLE_SIZE)
   target_compile_definitions(snmalloc_lib INTERFACE -DMALLOC_USABLE_SIZE_QUALIFIER=const)
 endif()

src/mem/threadalloc.h

@@ -19,6 +19,7 @@
 #  if defined(SNMALLOC_THREAD_TEARDOWN_DEFINED)
 #    error At most one out of method of thread teardown can be specified.
 #  else
+#    include <pthread.h>
 #    define SNMALLOC_THREAD_TEARDOWN_DEFINED
 #  endif
 #endif
@@ -95,7 +96,7 @@ namespace snmalloc
     }
   };
 
-#  ifdef SNMALLOC_USE_PTHREAD_DESTRUCTOR
+#  ifdef SNMALLOC_USE_PTHREAD_DESTRUCTORS
   /**
    * Used to give correct signature to teardown required by pthread_key.
    */

src/test/func/thread_alloc_external/thread_alloc_external.cc

@@ -1,3 +1,7 @@
+#ifdef SNMALLOC_USE_PTHREAD_DESTRUCTORS
+#  undef SNMALLOC_USE_PTHREAD_DESTRUCTORS
+#endif
+
 #include <snmalloc_core.h>
 #include <test/setup.h>